This invention relates to heat exchangers, and more particularly to the manufacture of heat exchangers.
It has previously been proposed to form heat exchangers by welding or brazing tubing on the surface that is to be heated or cooled. For example, in the case of turbogenerators with superconducting excitor windings, the excitor winding is cooled by liquid helium. The cold rotor body carrying the winding is installed within an external hot cylinder. The fastening of the inner rotor body and the transmission of torque to the shaft ends takes place through thin transition pieces which are also cooled by helium gas. Cooling could be accomplished by using cooling coils consisting of a spirally-wound tube which is welded, brazed or expanded onto the shaft ends. The disadvantage of this technique lies in the fact that the connecting seams between the tube and the shaft that is to be cooled are applied to a surface which is highly stressed, so that there is a danger that the joint between the tubing and the surface will separate. Such a joint is mechanically weak and does not provide good thermal conductivity between the cooling tube and the body that is to be cooled.
It is an object of this invention to provide a heat exchanger having relatively small cooling passages on the exterior of a larger body which can be manufactured efficiently and economically, and which has sufficient mechanical strength to withstand stresses between the cooling passages and the surface of the body.
This object is accomplished in accordance with a preferred embodiment of the invention by manufacturing a plurality of cooling passages on the exterior surface of the body. The passages when formed initially are open with outwardly projecting flanges. The flanges are then drawn together and welded to form closed passages integral with the base surface.